As discussed in U.S. Pat. Nos. 4,024,093 (Abolins et al.) and 4,670,537 (White) assigned to the same assignee as the present invention and incorporated herein by reference, polyphenylene ethers can be made by the oxidative coupling of a phenol in the presence of a metal amine complex catalyst. As shown by U.S. Pat. No. 4,670,537, polyphenylene ethers formed by the aforementioned oxidative coupling reaction can be substituted with chemically combined alkylamino end-groups. It is further shown in U.S. Pat. No. 3,383,435, Cizek, assigned to the same assignee as the present invention and incorporated herein by reference, that polyphenylene ethers can be blended with styrene resins over wide portions by weight to provide a wide variety of high performance thermoplastics.
Considerable effort has been made to improve the flame retardant properties of both polyphenylene ethers and blends thereof. Generally, various compounds, such as hexabromobiphenyl, and a metallic salt, such as an organic iron compound, for example, a ferric salt of an organic carboxylic acid, such as ferric stearate, have been used to impart improved flame retardant properties, particularly to polyphenylene ether blends without substantially reducing the impact properties of the resulting flame retardant thermoplastic.
The present invention is based on my discovery that polyphenylene ether substituted with alkylamino groups can be neutralized with a Bronsted acid, as defined hereinafter, to produce the corresponding polyphenylene ether Bronsted acid amine salt. Reaction can be effected in the presence of a substantially inert organic solvent between a Brosted acid and an alkylamino substituted polyphenylene ether. Surprisingly, blending of the resulting polyphenylene ether Broacid amine salt with polystyrene, or HIPS, followed by the extrusion thereof, as defined hereinafter, results in the production of extrudate having substantially improved flame retardant properties. The extrudate does not have to be further modified with an additional flame retardant. However, if V-0 flame retardant results are desired, in accordance with UL 94 Flammability of Plastics Materials for Parts in Devices and Appliances, June 1, 1973, a relatively small amount of a flame retardant, such as a brominated polycarbonate oligomer (FR-25) can be added to the blend, preferably prior to extrusion.
As used hereinafter, the term "extrudate" means a blend of polyphenylene ether amine salt and styrene resin which has been melt extruded in contact with a ferruginous surface.